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Comment by StillBored | Hacker News Reader

Ok, given its flying just the core, and not the fan, why doesn't it fit in the cargo hold? I mean they wouldn't have to worry about the extra drag/etc in the hold.

It also seems odd that they would do this on a plane carrying commercial passengers since it seems more of an "experimental" modification even if the manufacture has approved it.

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It isn't experimental or unique even if it's rare. It has been done before. I'm not sure why this instance alone got such attention.

Regarding the cargo hold problem, the aircraft wasn't carrying just the engine core. The 'pod' is most likely the engine nacelle itself. I wonder if the entire thing would fit through the cargo door (mere speculation). While it's true that the 747 was originally meant as a cargo carrier, most of it was meant to be loaded through the nose of the aircraft. The nose could be opened for this purpose and the cockpit was above the cargo area to accommodate this.

It got so much attention because it's rare. We like to read about things that seem novel and interesting. I wasn't aware the 747 had this capability until reading this article today.

Normaly the nose loading is done oy when absolutely necessary. It's a pain, takes ages and is complicated. When possible stuff is squeezed through the fuselage cargo doors. Back the day we did it with a ten foot sea container, never thought it would fit...

I agree about the nose loading part. Meanwhile, how does an engine with its nacelle compare to a marine container in terms of dimensions? Would it be easier or harder to load through the fuselage doors? I also assume that they will need a fixture or container for the engine if it was to be loaded into the cargo hold.

Engine is roughly 2.25m in diameter and 5.5m in length. So it would fit through the nose cone door, even with a modest fixture/container, with room to spare.

> Back the day we did it with a ten foot sea container, never thought it would fit

How’d you end up doing it? Roll it on its side? Usually the height of a sea going container is ~2.6m and per the specs I’m seeing online the allowed height through the nose is only ~2.49m. Because they are just taller than they are wide, spec wise it would fit laying on its side, but still curious when doing it for real if that was necessary.

Presumably they're talking about a 8x8x10 container. The 747 is specced for 8x8 w/h containers.

Yeah, 8’ just barely fits in via the nose. You got maybe an inch or two to spare on height.

Going via the main deck side doors on a cargo style 747 would be much easier imho for a container that size. Not only can you go a full 10ft high, you’ve got around 11’ straight in width clearance.

They maneuvered it through the side door, with four people, inch by inch, millimeter by millimeter. Working for the airport at the time I didn't touch a thing, better to have crew damage a perfectly fine aircraft. Still impressive feat of loading, almost on par with the Russians, they use the cargo door to squeeze the cargo properly in, like avergae Joe slaming his trunk.

Ah, side door. That should’ve been easy then, no?

> While it's true that the 747 was originally meant as a cargo carrier

I was surprised by this so I consulted Wikipedia. Apparently when the 747 was designed they were convinced enough that passengers in the future would not want to travel subsonically, so they designed the 747 to convert to a freighter, to not have to throw the design away when it's hard to attract passengers due to the "low" 0.8 mach speeds!

In general there was a time when supersonic flight was considered the future evolution that will displace the existing tech, like jets displaced propeller aircraft. The Concorde was supposed to be the first one, and it was designed as a general use plane, it wasn't until much later British Airways and Air France thought about marketing it for business/first class "luxury" experience.

For a myriad of reasons ( Boeing failing to make their own supersonic airliner which helped the US Congress banning supersonic flights over the US being one of them), we never got there though, and it seems we never will since the currently planned crop of supersonic airliners ( Boom and co) are specifically targeting the business niche.

> Boeing failing to make their own supersonic airliner which helped the US Congress banning supersonic flights over the US being one of them

You sure about that order? I thought supersonic domestic flights got banned in the US and then the Boeing supersonic airliner was doomed. I’m not positive, hence asking.

Nope, government funding of Boeing's SST was cut in 1971, while the SST ban over the US was enacted in 1973. It's fairly certain that had Boeing made an SST there wouldn't have been any ban.

Thanks! I only knew the oft parroted version of the story from family members who worked at Boeing. I guess the detail I didn’t immediately recall was “plane over budget” (which likely lead to the government funding you mentioned being pulled). I still believe that the biggest reason for the ban was NIMBYs though, if you’ve ever been around sonic booms you know how intrusive they are. I lived just far enough away from a military base as a kid that we happened to be near where pilots would occasionally go super sonic as part of their training. After living in California years later and experiencing multiple earthquakes, I’d say the sonic boom was about like a magnitude 6, but only lasting for a couple seconds.

Isn't the main reason the amount of fuel required to fly supersonic?

The designs did burn a lot of fuel, but sonic booms were also extremely unpopular.

The FAA picked Oklahoma City (without asking them first) for an experiment to subject a city to regular sonic booms. It, uh, didn’t go well. https://en.m.wikipedia.org/wiki/Oklahoma_City_sonic_boom_tes...

Right, but what I meant was that it'd be difficult to have a sustainable supersonic flight business given the fuel consumption required at those sppeds. My understanding is that even though Air France and British Airways were charging twice the price of normal first class for Concord, they were losing money on them.

I'm surprised there aren't supersonic business jet though.

> My understanding is that even though Air France and British Airways were charging twice the price of normal first class for Concord, they were losing money on them.

They weren't, the Concordes were quite profitable until 9/11 and the following slump in international travel ( due to fear, increased controls and inconveniences) and increase in oil prices.

> I'm surprised there aren't supersonic business jet though

There are companies trying to build supersonic business jets, like Boom.

It was a novelty. The market was small the expectation that it costly but still profitable is easy.

But I wouldn't care for sonic travel besides the novelty.

Price wins

Admittedly for a unique minority Concorde wasn't a novelty at all: the very few journalists who covered Washington and London global political developments (and who were indulged the budget) used Concorde more often than any red eye shuttle. I actually associate the atrocious decline in public US - UK understanding to this absurdity. The absurdity being how much we needed a humanist perspective on transatlantic relations after 9/11 but got informationally waterboarded instead by sheer volume of grade school quality wire release. The cost of running Speed Bird even a little longer for diplomatic corps reporting should have been a mutual national priority.

Also, that happened to be right around the end of their lifespans anyways, and no one wanted to invest in a second generation plane.

If curious what a sonic boom sounds like. I found this video.

https://www.youtube.com/watch?v=M_KbZON5sW0

The normal caveat about how microphones are really unable to capture sounds of this magnitude probably apply here.

For example, I once went to vandenburg to see a rocket launch and that was the biggest sound I have ever heard, not the loudest, we were five miles away, but the way the sound shook you impressed the hell out of me.

Indeed, the 747 is quite popular amongst cargo carriers.

In comparison, part of the A380’s short life is that it’s useless as a freighter since a minimal amount of freight would bring it to “too heavy to fly” territory.

It's a design feature dating back to when there were no easy ways to transport the engines. It's a perfectly cromulent way to transport a 747 engine, just uncommon these days because there are many large air freighters now (like the 747 itself). The idea was that in the early days of the 747, airlines could be self sufficient in transporting engines and their new expensive planes wouldn't get stranded.

It should be noted in context that original the 747 could, like the 737 before it, service airfields too small to have service centers. Therefore, it was important that another 747 could ferry in all parts needed to service a potentially damaged 747 at these locations, including an entire engine.

Most aircraft with such capability are identified by the inclusion of built-in stairs for passenger ingress/egress, which the 747-100 had.

The 737-200 had an optional gravel kit for unpaved runways! A few -200s still in use because of that feature

Neat - kind of like mid flaps for planes. Also thank you for teaching me a new word, "cromulent".

I am dating myself but I'm old enough to have watched the Simpsons episode where this word was invented in its first airing. Maybe it is a word now, I mean it's no more or less ridiculous than other words, which somebody just made up at some point too.

https://www.merriam-webster.com/words-at-play/what-does-crom...

You're embiggening my perception of you.

The issue is the dimensions of the cargo doors. A 747 engine is approximately 2.25m in diameter and 5.5m long. Of the 4-5 different sized doors on a 747, there’s only two that it would fit through:

- Front nose cone door

- Main deck cargo door

I believe neither would be used on a passenger airline configured 747 (could be wrong though!) and hence why the wing based fifth pod configuration was likely used.

Wikipedia puts the CF6 from a 747-400 at 4.27m long, 2.69m diameter. An RB-211 looks to be a little narrower and longer. Cargolux puts the biggest rectangle that can fit through the main cargo door at 3.05m x 3.10m. So yeah you could probably fit an engine in a nacelle and fixture through the main deck door on a freighter.

However your big limitation will be height at either 2.44m or 3.00m depending on where on the main deck you're checking. The lower deck (which is all you'd have available on a passenger 747) has a much lower height limit (an LD-1 has a height limit of 1.62 m).

An engine's just not going to fit inside unless you're talking about something designed for oversize cargo like the Dreamlifter (747) or Beluga (A300) or Beluga XL (A330). Oversized cargo is also the main use case for the An-124/225.

https://www.cargolux.com/fleet-equipment/aircraft/747-400f-s...

> An engine's just not going to fit inside unless you're talking about something designed for oversize cargo like the Dreamlifter (747)

This is in direct conflict with literally the paragraph you posted before it. You could definitely carry the RB-211 on a standard cargo version of the 747, as you yourself stated previously. It could only fit on the main deck, but the standard 747 cargo (aka not needing the guppy) definitely could do it.

Yeah there's about 0.7 m more height than a CF6. That seems like potentially not enough room for a proper fixture. In any case it's not going to fit inside a passenger 747.

It's rare to see a car pulling a trailer, but it's not experimental.

The "fifth pod" thing was designed in from the start.

The trailer thing is sorta exactly why I'm uncomfortable with it.

I have a truck which a few times a year I tow various trailers/etc with. Yes the truck was "designed" for this, but that doesn't mean its not eating in safety margins in many ways and is fundamentally far more dangerous for a laundry list of reasons over simply driving the truck around.

The asymmetry of something that large is going to create a lot of complications that this article is glossing over with "trimming", starting with weight/balance issues (which presumably end up being a case that the opposing wing tanks need to be unbalanced/over full, and managed by the crew, etc), and unusual airframe/control surface stresses that eat into the engineering margins.

So, it wouldn't be noteworthy except for the fact that they were also flying 350+ passengers at the same time. Many airline accidents are cases of confounding variables strung together. You can be assured that had anything unusual happened on that fight, that the NTSB report would have started with "The airplane was flying massively out of trim"

Well it is carrying the core and the nacelle. The nacelle is the bulkiest part.

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